An Optimization Method Of Automated Speed Camera Layout Using GPS Trajectory Data

In China,the number of traffic accidents and the loss of life and property caused by speeding have been in the forefront of all kinds of traffic violations.At present,it has basically formed the situation of"taking automated speed camera as the main part and other intervention measures as the auxiliary"to intervene speeding.However,the existing installation locations of automated speed camera（ASC）are mainly evaluated and judged based on the historical experience.Therefore,it is necessary to optimize the location and number of ASCs under the condition of considering the influence range of the distance halo effect of ASC.In this paper,the GPS trajectory data along the North Exit freeway and six continuous cross intersections installed with ASC located in the city center in Chengdu,China were collected from November5^thto November 18^th,2016.Based on the fusion of GPS trajectory data,relevant information of geographic data and ASC positions,the distribution characteristics of delta speed（the difference between the traveling speed and the speed limit）in different driving directions in research scope were disclosed.The propensity score matching method was then used to determine whether the installation of ASC has a significant deterrent effect.Through the K-means clustering,the critical delta speed values in each driving direction of the road segment and intersections were acquired,and the corresponding distance halo effects of ASC were obtained.Meanwhile,the upstream and downstream distance halo effect of each ASC and the superposition of the adjacent ASC distance halo effect were explored.Finally,the number and positions of ASC are optimized according to the research results.The results show that the higher the speed limit value of road segment is,the higher the delta speed corresponding to the peak value of kernel density estimation of the GPS trajectory points.However,within the intersections,the lower the speed limit value of road segment is,the higher the delta speed corresponding to the peak value of kernel density estimation of the GPS trajectory points.Within the range of road segment,the deterrent effect of ASCs in the eastbound direction is not significant,but its in the westbound is significant.At the same time,ASCs in both directions have a significant deterrent effect within the intersections.On the whole,regardless of the road segment and intersections,with the increase of the number of ASCs,the upstream distance halo effect of the ASC has been gradually enhanced,while the downstream distance halo effect of the ASC has been gradually decreased.Nevertheless,from the perspective of the relationship between adjacent ASC,the superimposed influence range of downstream distance halo effect of the first ASC and the upstream distance halo effect of the second ASC in the eastbound direction is about 1600-1900 meters.In the westbound direction,there is no superposition between the downstream distance halo effect of the first ASC and the upstream distance halo effect of the second ASC.The superposition range of the downstream distance halo effect of the second ASC and the upstream distance halo effect of the third ASC is about 1700 meters.Within the range of the intersections,the duration range that the downstream halo effect of ASC is stronger than that of the upstream is stable within about1600-1700 meters.Finally,according to the distribution characteristics of delta speed and the results of distance halo effect of ASC,the number and positions of ASC in two driving directions of road segment and intersections were optimized,respectively.